Many organic pigments do not have an appropriate particle size distribution as recovered from chemical synthesis to be directly used in pigmentary applications so it is necessary to "condition" them. U.S. Pat. No. 2,816,114 outlines the three main approaches which the art had taken; acid pasting; salt milling and solvent milling. This patent and U.S. Pat. No. 2,982,666 proposed alternative techniques which avoided the necessity of utilizing a ball mill but these techniques still generally required a solid grinding aid. The former patent particularly emphasized borax whereas the latter utilized sodium chloride, urea, sucrose and sodium sulfate in its examples. Example 32 of the U.S. Pat. No. 2,982,666 does appear to report the conditioning of a phthalocyanine pigment by intensive mixing in a Banbury device using just a polyethylene glycol medium. However, it is evident from U.S. Pat. No. 3,748,164 that later workers generally viewed the teachings of the U.S. Pat. No. 2,982,666 as interesting only when a "grinding aid" was utilized. This patent proposed a certain class of tackifying agents for use in this salt grinding process. More recently in U.S. Pat. No. 4,298,399 it has been proposed to salt grind in a medium of corn syrup, corn syrup solids or molasses.
The present applicants have surprisingly found it possible to suitably condition organic pigments without the use of a solid "grinding aid" such as salt and without the need to use masticator machines of the heavy duty dispersion mixer type (Banbury or Baker-Perkins type, for example) required by the U.S. Pat. No. 2,982,666. In fact, they have found a technique which allows the use of the sigma double arm mixers which are specifically identified as unsuitable in this patent at column 5, lines 17 to 20.